Japanese Laid-open Patent Publication No. 2005-223999 discloses an electric power control device which includes a rectifying part which converts alternating electric power of a power supply into direct electric power; a capacitor connected to the output side of the rectifying part; an inverter which converts the direct electric power of the capacitor into the alternating electric power; and a collective controlling part which includes a PWM switch circuit connected to the rectifying part in parallel, wherein the collective controlling part has a harmonics removing function and an electric power regenerating function. The collective controlling part functions as an active filter to remove the harmonics of the alternating electric power of the power supply if the voltage of the capacitor is lower than a predetermined value, and functions as a power regenerating converter to supply the electric power of the capacitor to the power supply if the voltage of the capacitor is higher than the predetermined value.
However, if the PWM switch circuit is simply connected to the rectifying part in parallel as is the case with the prior art described above, a return path of the current flowing through the rectifying part is formed in the PWM switch circuit. This current is called a circulating current, and the circulating current causes power loss.